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Here is the customer question that came into Scott and his reply:

 'One question for you...

In setting up the braking on this...  what kind of specs do I want to use to get the fastest stopping and starting, without taxing the drive and motor? 

The motor is a Doerr 1hp, and the label shows it at a 208-230v but only shows one amp rating (expected two for the different voltages) of 3.8 amps. 

I'd really like it to slow down pretty good, but not wanting to mess with the braking resistor for the time being... so trying to figure out what I should realistically be able to do as far as Accel and Decel times and if upping the amps a little (say setting the max output to like 4 or 5 amps instead of the 3.8 that is on the data plate) might help a little one way or another and not harm the drive.

Thanks again for all the help, and you guys being faster than you thought'

Our answer: (Special note: if you need more information or have a similar question our tech department can help you as well!)

I can’t really give any values for this because it is application specific.

The key factors include:

1)            Reflected mechanical inertia from the motor

2)            Peak braking power required for stopping the motor/load and the time required from full speed to a decelerated stop.

3)            RMS power (P-rms) based on the voltage regenerated by the motor caused by this reflected inertia during braking.

1)    Ideally you need to know what the reflected mechanical inertia is from the motor. From there you can determine the average power (Pave) based on this reflected inertia.

The basic formula is Pave = KE (kinetic energy) / Tb. Tb is the required deceleration time. Smaller Tb means more average power needed to stop the load.

The KE is 0.5 * Ji * (Ws squared) where Ji is the inertial load and Ws is the synchronous speed.

2)    This is not usually an easy value to obtain. So, what typically is done is make sure the duty cycle does not exceed our ratings which are for light duty braking or 4 to 5%. This refers to the time the braking

circuit is on (Tb) vs. the complete cycle time (Tc) or duty cycle = Tb/Tc. So, if dynamic braking is on for 3-seconds during a 1 minute cycle time, the duty cycle is 3/60 =5%.

3)    The other important factor is the dynamic braking module's current limit. Fortunately the sub-micro drives can have DB modules placed in parallel to reach higher current demand. However, some care needs to be

taken to not exceed the maximum current of the connector between the drive’s and the DB module’s B+/B- terminal block.

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